Fluid springs



Jan. ll, 1966 E. WSTENHAGEN l FLUID SPRINGS Filed May 8, 1963 Ard ....r um A, l.

/7 Mw//Z 7 INVENT'L;

Ems r WiLSTaN H AGEN MQMJ Mm United States Patent O 3,228,674 FLUID SPRINGS Ernst Wstenhagen, Koblenz, Germany, assignor to Stabilus Industrieund Handelsgesellschaft m.b.H., Koblenz- Neuendorf, Germany Filed May 8, 1963, Ser. No. 278,949 Claims priority, application Germany, May 14, 1962, St 19,235 4 Claims. (Cl. 267-65) In known fluid springs, the spring properties depend, apart from purely structural dimensions, on the compressibility and elasticity modulus of the fluid used at the relevant pressure, and the operating temperature also has an influence on these properties. In a typical example, a mineral oil or silicone oil may be employed as the fluid in this type of spring.

It is an object of the present invention to improve the spring properties of such fluid springs and to obtain a certain damping effect. This problem is solved by providing an arrangement wherein pressure variations produced by reciprocation of the plunger of the fluid spring in a working space are passed into a plurality of annular chambers surrounding the working space. The working space is in communication with the annular chambers through the intermediary of passages, metal filters and resilient means which may be employed in different combinations with one another, the various annular chambers being interconnected or sealed off from one another as the case may be by similar means.

The fluid spring according to the present invention is filled with a fluid under a pressure on the order of 2,000 to 5,000 atmospheres absolute pressure. Due to this high pressure, the plunger of the spring is forced out of the spring. In order to restrict this undesirable side effect to a predetermined extent, the plunger is in the form of a differential plunger. This construction enables the annular effective surface of the plunger to be adapted to prevailing conditions. This was basically impossible with conventionally shaped plungers since there is a lower limit to the diameter of the plunger arising from considerations of mechanical strength.

It is advantageous for the housing of the fluid spring to be made of a material, such as aluminum, the thermal expansion of which is substantially the same as that of the spring fluid.

The invention is described hereinafter with reference to one form of the invention as illustrated in the single figure of drawing which is a diagrammatic representation in longitudinal section of the fluid spring according to the present invention.

In order to emphasize the inventive concept, details of the fluid spring which are not essential to an understanding thereof, such as seals and the like, are not included in the drawing.

Referring now to the drawing, a spring plunger 1 is reciprocable in the working space 2, and the working space is surrounded by annular chambers indicated by reference numerals 3, 4, 5 and 6, and these chambers may be of the same or different sizes. One or more of the annular chambers may be directly connected to the Working space 2 by means of passages 7. These annular chambers may also be interconnected with the working space through the intermediary of metal filters 8 or resilient means indicated `by reference numeral 9. The chambers 3, 4, 5 and 6 may either be sealed oil from one another or interconnected with one another in a similar Barrantes! Jan- 11, 19626 manner to that in which the various chambers are interconnected With the working space. Chambers 3 and 4 are preferably sealed off from one another as shown. In this manner, the pressure variations caused by reciprocation of the spring plunger 1 and the working space 2 are directly or indirectly brought into communication with the chambers in question.

The passages 7 are ordinaryapertures suitably dimensioned according to the conditions of operation, and the metal filters 8 which are metallically connected to the housing of the spring may be made of powder which is metallurgically produced, porous metallic materials of all kinds, and so-called porous sintered materials, particularly bronze powder or iron or 18/8 chrome-nickel-steel powder in pellet form.

The resilient means 9 may comprise rubber cushions, or fluids such as air or the like which is more highly compressible than the spring fluid used which may be a mineral oil or a silicone oil as is conventional in the art.

The metal filters 8 of the present invention are provided to give a damping effect to the spring due to the constricted passage through the pores of the metal filters, and these metal filters do not actually act as filters, but serve to produce a flow resistance acting as a throttle and also serving the function of conducting heat away from the apparatus which results from the damping eflect.

When highly compressible fluids are employed as the resilient means 9, these fluids may be separated from the spring fluid in a known manner as for example by an elastic partition wall, a roller bellows or the like. The resilient means 9 must not be used only for connecting the working space 2 directly to an annular chamber, but instead must also be mounted in one or more of the annular chambers 3, 4, 5 or 6 in any suitable manner. Thus, for example, a roller bellows, acting as a resilient means 9 to enclose a highly compressible fluid and separate it from the spring fluid, may preferably be arranged in any suitable manner in the annular chamber 4.

The present invention is not restricted to the example described and illustrated, but also covers all combinations of the various components, and in particular encompasses different arrangements of the apertures 7, the filter plates 8 and the resilient means 9. Accordingly, a passage or aperture 7 may be located in a metal filter 8 as illustrated between annular chambers 4 and 5, and the number of annular chambers may be more or less than 4 as desired.

I claim:

1. A fluid spring which comprises cylinder means, a stepped differential plunger slidably mounted in said cylinder means, means defining'an annular chamber extending around said cylinder means, at least two porous metal filters dividing said cylinder into at least three annular sub-chambers, resiliently compressible means being provided in a first sub-chamber and at least two apertures being provided in the walls of said cylinder in communication with said second and third sub-chambers respectively, said cylinder means and said sub-chambers being lled with liquid whereby, when the plunger is at the beginning of its stroke, pressure is applied to said resilient means by the liquid through one filter and at a later stage in the plunger stroke when the plunger has closed at least one of the apertures in the cylinder Wall, pressure is applied to the resilient means by the liquid through at least two filters.

2. A fluid spring according to claim 1, wherein said resiliently compressible means comprises a uid more highly compressible than said liquid.

3. A iluid spring which comprises cylinder means, a

stepped differential plunger slidably mounted in the cylinder means, means defining an annular chamber extending around the cylinder means, three porous sintered metal filters spaced axially within said chamber and delining four annular sub-chambers, the second and fourth sub-chambers being in communication with ythe interior of said cylinder through apertures in the wall of said cylinder and the second and third sub-chambers being in free communication with each other through an aperture in the filter between them, a resiliently compressible pocket of gas in the first sub-chamber, and liquid filling the remainder of the cylinder and the annular chambers.

4. A fluid spring which comprises a cylinder means, a differential piston slidably mounted in said cylinder means, means defining an annular chamber extending around said cylinder means and in communication therewith, resilient means in said chamber, porous sintered metal filter means interposed between said resilient means and said cylinder means and liquid at 2,000 to 5,000 atmospheres absolute pressure in said cylinder means and in said chamber for conveying pressure applied by said piston to said resilient means through said filter means,

References Cited bythe Examiner UNITED STATES PATENTS 2,581,856 1/1952 Gruss 267-64 2,635,715 4/1953 Riedel et al. 18S-100 2,701,583 2/1955 Rux 188-100 2,771,968 11/ 1956 Mercier 267-64 2,873,964 2/ 1959 Hamilton 267-64 2,960,289 11/ 1960 Westcott 267-64 2,984,478 5/1961 Westcott 267-64 2,989,299 6/ 1961 Modrich.

3,076,643 2/1963 Bittel 267-64 3,087,717 4/1963 Jewell 267-64 FOREIGN PATENTS 641,527 8/ 1950 Great Britain. 1,036,073 8/1950 Germany. 1,040,913 10/ 1958 Germany.

ARTHUR L. LA POINT, Primary Examiner. EUGENE G. BOTZ, Examiner. 

1. A FLUID SPRING WHICH COMPRISES CYLINDER MEANS, A STEPPED DIFFERENTIAL PLUNGER SLIDABLY MOUNTED IN SAID CYLINDER MEANS, MEANS DEFINING AN ANNULAR CHAMBER EXTENDING AROUND SAID CYLINDER MEANS, AT LEAST TWO POROUS METAL FILTERS DIVIDING SAID CYLINDER INTO AT LEAST THREE ANNULAR SUB-CHAMBERS, RESILIENTLY COMPRESSIBLE MEANS BEING PROVIDED IN A FIRST SUB-CHAMBER AND AT LEAST TWO APERTURES BEING PROVIDED IN THE WALLS OF SAID CYLINDER IN COMMUNICATION WITH SAID SECOND AND THIRD SUB-CHAMBERS RESPECTIVELY, SAID CYLINDER MEANS AND SUB-CHAMBERS BEING FILLED WITH LIQUID WHEREBY, WHEN THE PLUNGER IS AT THE BEGINING OF ITS STROKE, PRESSURE IS APPLIED TO SAID RESILIENT MEANS BY THE LIQUID THROUGH ONE FILTER AND AT A LATER STAGE IN THE PLUNGER STROKE WHEN THE PLUNGER HAS 